1. Field of the Invention
The present invention relates to macromolecular type liquid crystal elements used in a diffusion plate of a camera and the like. More particularly, the present invention relates to a liquid crystal element which can control diffusivity with a low driving voltage.
2. Description of the Related Art
Conventionally, macromolecular liquid crystal elements are incorporated into a structure in which a macromolecular dispersion type liquid crystal is interposed between transparent electrodes, such as indium tin oxide or the like, disposed on the surfaces of two (2) flat transparent plates. The diffusivity in the known macromolecular dispersion type liquid crystal element is regulated by changing between a diffusing state and a transparent state by controlling an alternating voltage or the like applied between the transparent electrodes.
However, when the diffusivity of the prior art macromolecular dispersion type liquid crystal element is increased in the above-described manner, the film thickness of the macromolecular dispersion type liquid crystal layer must be thick. When the film thickness is made thick, the spacing of the transparent electrodes becomes wide, and the driving voltage becomes high.
Moreover, the known macromolecular dispersion type liquid crystal element diffuses light to some degree even when a voltage is applied. Therefore, when the film thickness of the liquid crystal layer is made thick, the optical transmissivity in the transparent state becomes poor, and the contrast between the diffusion state and the transparent state falls off.
Moreover, when the known macromolecular dispersion type liquid crystal element is applied to the diffusion plate of a camera or the like, it becomes difficult to obtain more diffusivity in the diffusion plate because the diffusivity of this element depends on the properties of the macromolecular dispersion type liquid crystal. More specifically, in prior art diffusion plates, because diffused light remains having a diffusion coefficient which is increased to some extent, a so-called "soft focus" image is obtained such that fogginess faintly surrounds a blurred image, even in a region in which the angle from the normal line is rather large.
FIG. 6 is a graph showing the diffusion coefficient of a prior art type of diffusion plate. The prior art diffusion plate includes a plane parallel plate glass, which is unaltered and has no roughness formed on it, used as a glass plate, and both interfaces with the macromolecular dispersion type liquid crystal are flat. In the prior art diffusion plate, as an angle .theta. from a normal line to the diffusion plate becomes large, the diffusivity of the diffusion plate gradually becomes small, and diffusivity remains to some degree, even in regions in which the angle .theta. is quite large. Further, in the prior art type of diffusion plate, when an image projected thereon is indistinct, the so-called "soft focus" image is obtained, with fogginess extending widely around a blurred image.